1. Technical Field
This invention relates generally to wireless communication systems; and more particularly to load assignment and dynamic load balancing within a multiple carrier frequency wireless communication system.
2. Related Art
Cellular wireless communication systems are generally known to include a plurality of base stations dispersed across a geographic service area. Each of the base stations includes at least one antenna and a base station transceiver system (BTS) and provides wireless service within a respective cell. The BTSs couple to base station controllers (BSCs) with each BSC serving a plurality of BTSs. The BSCs also couple to a mobile switching center (MSC) which interfaces to the Public Switched Telephone Network (PSTN) and other MSCs. Together, the BTSs, BSCs and the MSC form a wireless network which provides wireless coverage to mobile units operating within a respective service area.
Wireless communication systems operate according to various standards. One particular standard in place worldwide is the code division multiple access (CDMA) protocol. Code division multiple access (CDMA) is a direct sequence spread spectrum system in which a number, at least two, of spread-spectrum signals communicate simultaneously, each operating over the same frequency band. In a CDMA system, each user is given a distinct Walsh code which identifies the user. For example, if a first user has a first chip code, g.sub.1 (t), and a second user a second chip code, g.sub.2 (t), etc., then a receiver located in a BTS, desiring to listen to the first user, receives at its antenna all of the energy sent by all of the users. However, after despreading the first user's signal, the receiver outputs all the energy of the first user but only a small fraction of the energies sent by the second, third, etc., users.
CDMA is interference limited such that the number of users that can use the same spectrum and still have acceptable performance is determined by the total interference power that all of the users, taken as a whole, generate. Thus, the number of users that may be supported by each BTS is limited. To increase the capacity of CDMA systems, additional base stations may be added to increase the number of cells within the service area. However, because load is often concentrated in a small geographic area, even with the addition of cells, particular cells may remain overloaded while neighboring cells are lightly loaded.
Thus, another solution has been proposed to overcome overcrowding in CDMA systems. This solution includes assigning multiple carriers within a single service area with the multiple carriers used to service overlaying cells. With overlaying frequency coverage, some mobile units are serviced on one of the carrier frequencies while other of the mobile units are serviced on other of the carrier frequencies. By assigning multiple frequency resources, the overall capacity of the wireless communication system is increased.
However, due to the nature of accessing the CDMA system and assigning resources in the CDMA system, one frequency may tend to become loaded at a rate greater than the other frequency. Thus, there is an inherent problem in such wireless communication systems in properly allocating usage amongst the multiple carrier frequencies to maximize carrier traffic for a given blocking probability.
Thus, there is a need in the art for a system and associated method of operation for allocating load amongst multiple carrier frequencies in a multiple carrier frequency system and in balancing load in the multiple carrier frequency system.